Q1(h). Ammonia buffer

Answer in brief

A buffer resists modest pH changes on adding small amounts of acid or base; the NH₃/NH₄⁺ pair consumes the added reagent.

Key points

• Aqueous ammonia is a weak base and ammonium chloride supplies its conjugate acid. The equilibrium is NH₃ + H₂O ⇌ NH₄⁺ + OH⁻.
• Added acid is consumed by NH₃ + H⁺ → NH₄⁺. Added base is consumed by NH₄⁺ + OH⁻ → NH₃ + H₂O.
• Approximately pH=pKₐ(NH₄⁺)+log ([NH₃]/[NH₄⁺]). Small additions change the ratio only slightly when both buffer components are present in substantial amounts.
• Buffer capacity is finite; large additions exhaust a component. Dilution approximately preserves the ratio but lowers buffer capacity.